Minor tweak to improve performance of ActiveRecord::Base#to_param

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4531 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

 *SVN*
 
+* Minor tweak to improve performance of ActiveRecord::Base#to_param.
+
 * Observers also watch subclasses created after they are declared. #5535 [daniels@pronto.com.au]
 
 * Removed deprecated timestamps_gmt class methods. [Jeremy Kemper]

activerecord/lib/active_record/base.rb

@@ -1441,7 +1441,7 @@ def id
       # Enables Active Record objects to be used as URL parameters in Action Pack automatically.
       def to_param
         # We can't use alias_method here, because method 'id' optimizes itself on the fly.
-        id.to_s if id # Be sure to stringify the id for routes
+        (id = self.id) ? id.to_s : nil # Be sure to stringify the id for routes
       end
 
       def id_before_type_cast #:nodoc: